1. Field of the Invention
The present invention relates generally to the field of semiconductor device fabrication and, more particularly, to wafers having vias formed therein. Methods of forming vias, including vented vias and vias filled with conductive material and having conductive elements thereon are also included.
2. Background of Related Art
Semiconductor chips may be produced with integrated circuits on one or (less commonly) both sides of the chip and may be designed to connect to or interact with other electronic components or other semiconductor chips. Interposers may be utilized for interfacing two electrical components, such as a semiconductor device and a printed circuit board, and contactor boards may be used to interface a semiconductor wafer and a probe card for testing the dice on the semiconductor wafer. Semiconductor chips may be formed of semiconductor wafer or other bulk semiconductor substrate material, while interposers and contactor boards may be formed of silicon, ceramic or polymeric materials.
Through-holes, or vias, which have been conductively lined or filled are typically used for connecting an integrated circuit on one side of a chip to conductive traces on the other side of the chip, a ground or other bias voltage, another electronic component or an integrated circuit on another chip. Vias are also used for providing electrical communication between structures disposed on opposing sides of an interposer or contactor board, wherein the structures may align with contact pads or other structures of electrical components and establish electrical connection between the various components.
Vias may be filled with conductive material in the form of solder. The via sidewalls may be coated with flux, such as hydrochloric acid or borax, to prevent oxides from separating the solder from the sidewalls. A solder paste, which may be as much as 50% flux, may be used to fill the vias, then heated to reflow the solder paste. During the heating process, one or more pockets of flux gases may form within the solder. Such pockets may cause the solder to expand outside the via. Solder expanding outside the via may touch an adjacent via or other conductive element and, thus, create a short circuit. When the pocket of flux gas is unable to escape, a void is created. If large enough, these voids can compromise reliability in the systems they inhabit by impairing an electrical connection or providing a connection which may fail later during use. A hole may be laser-drilled to the bottom of a blind via to provide a vent for the flux gases; however, this requires an additional processing step and additional equipment.
Conventionally, preformed solder balls may be positioned over the end of each via, and heated to reflow and attach the solder balls to the conductive material of the via. The contact between the conductive material of a via and a solder ball may create a brittle solder joint line susceptible to failure. Solder bumps may be formed or placed on the via in many ways, including evaporation, electroplating, printing, stenciling, jetting, stud bumping, and direct placement.
Accordingly, a need exists for a method of forming vias having a vent to release solder flux gases. Being able to form solder balls on vias without a brittle solder joint line therebetween would also be useful.